Renal ultrasonography was performed on 17,941 healthy adults without any signs suggestive of urinary tract malignancies. Diffusely hyperechoic renal masses indicative of angiomyolipoma were found in 41 (0.23%) of them and those with echogenic image suggestive of renal cell carcinoma in 45 (0.25%). Final diagnosis of the former group included 24 angiomyolipoma, 1 renal cell carcinoma, 9 calculus and 7 normal variants. The latter group included 19 renal cell carcinomas, 1 leiomyoma, 1 cavernous hemangioma and 24 normal variants or cysts. In total, 24 (0.13%) angiomyolipomas, 20 (0.11%) renal cell carcinomas, 1 leiomyoma, and 1 cavernous hemangioma were discovered. The results indicate that asymptomatic benign renal tumors mainly consisting of angiomyolipoma are not uncommon.